Quadratic Inequality

For any real numbers $\alpha$ and $\beta$, $\alpha<\beta$.

1. If $(x-\alpha)(x-\beta)\ge 0$, then we have
   \begin{equation*}
   x\le\alpha\mbox{ or }x\ge\beta.
   \end{equation*}

2. If $(x-\alpha)(x-\beta)\le 0$, then we have
   \begin{equation*}
   \alpha\le x\le \beta.
   \end{equation*}

Same Topic:

1. Definitions Basic Laws of Inequality Identities of Squares Measurement of Sound